Multiple strikes are often hard to spot when no movement of the
coin occurs between strikes. Collectors rely on a number of diagnostic
clues to identify such “close multi-strikes.” One such clue is the
presence of concentric strike lines.
Concentric strike lines are circular or semicircular grooves or
steps produced by the edge of the field portion of the die and
sometimes the outer edge of the rim gutter of the die. An intermediate
strike line can reflect the presence of collar clash, which occurs
when the rim gutter is damaged by contact with the top of the collar.
Close examination of spacing, contour and stepwise elevation of the
strike lines is necessary to distinguish those created by multiple
strikes from those that simply result from contact with different
parts of the die perimeter.
Strike lines are located in the “slide zone” of off-center and
broadstruck coins. The slide zone forms as coin metal squeezes out
between the dies and picks up fine radial striations in the process. A
strike line interrupts these striations.
It would be nice if strike lines always indicated the presence of
extra strikes, but this is not the case. For example, they sometimes
form opposite a “stiff collar” error. The planchet represented by the
illustrated 2000-P Jefferson 5-cent coin was not perfectly centered in
the striking chamber when it was struck. The right side rested against
a stiff, but still mobile collar. The obverse face (struck by the
anvil die) was left with a sloping, featureless shoulder that
terminates laterally in a strong collar scar. On the reverse face,
four concentric strike lines can be detected between the edge of the
field and the unstruck portion of the planchet.
The multiple strike lines were produced early in the downstroke as
the hammer (reverse) die skittered across the surface of the planchet
as the collar collapsed.
These strike lines happen to be a minor expression of a Type I
stutter strike. Had the bounces been higher and wider, a thin crescent
of die-struck design would have been left in the gap between the inner
and outer series of strike lines. A Type I stutter strike is shown in
the Dec. 28, 2009, “Collectors’ Clearinghouse” column.
I’m not sure what caused the extensive series of strike lines
present on the obverse face of the illustrated 1993-P Washington
quarter dollar. The broad crescent on the left carries no fewer than
six concentric lines. I doubt they represent an incipient stutter strike.
On the reverse face, strangely distant from the die-struck design,
are two short but very deep arcs of collar contact, located at 6:00
and 8:30. At this distance, I’m skeptical that the collar could have
provided sufficient resistance for even a loose hammer die to skitter.
This hypothesis would also have to incorporate the unlikely assumption
that the hammer (obverse) die contacted the planchet in a very
misaligned position and that it skittered its way to a centered
position by the time the downstroke was completed.
An equally dubious scenario has the planchet squeezing out beneath
a jittery hammer die. Instead of a “slide zone” forming with
conventional radial striations, a series of partial rings was
generated. The stumbling block here is that this presumptive slide
zone is far too wide relative to the strength of the strike, which was
quite modest. The slide zone on the reverse face is extremely narrow.
Almost as puzzling are the two to three concentric strike lines
present on the left side of the reverse face of a broadstruck 1998-D
Roosevelt dime. The coin shows are no signs of collar contact at all,
which would seem to rule out a Type I stutter strike. Here, at least,
it seems possible that the planchet squeezed out beneath a jittery
hammer (reverse) die, leaving a series of curved lines.
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